Development of the mouse circadian pacemaker: Independence from environmental cycles

Abstract

Summary 1.The freerunning period (τ) of the circadian pacemaker underlying the wheel-running activity rhythm of Mus musculus was found to be unaffected by the periods of environmental cycles (maternal and light/dark) under which the mice are raised. Mice born to mothers entrained to periods (T) of 28 or 20 h (ratio of light to dark of 14/10) and maintained on those cycle until beyond puberty showed only a temporary difference in freerunning period when placed into constant darkness. Such temporary 'after-effects ' of entrainment were shown, as had been previously, to occur in animals exposed to non-24-h cycles as adults only. 2.After-effects on the ratio of activity to rest (α/ρ) were not even temporarily different in animals raised on T = 28 or T = 20. 3.Rearing on T = 28 or T = 20 did not affect the abilities of animals to entrain to these cycles later in life. 4.Measurements from young and old animals as well as remeasurement of the young animals later in their lives revealed several effects of age on the pacemaker: a) Aftereffects on freerunning period after T = 28 or T = 20 are not greater but last longer in older animals; b) Freerunning period is shorter in younger animals; and c) The ratio of activity to rest changes over time in constant darkness and is greater in young animals. Together these suggest that pacemaker 'plasticity' reflected in changes in τ and α/ρ over time in constant darkness decreases with age. 5.The length of gestation measured in 'real' time was the same in mice entrained to T = 28 or T = 20, demonstrating that gestation is not measured in circadian cycles.

Decreased melatonin secretion is associated with increased intestinal permeability and marker of endotoxemia in alcoholics

“…Although our AD subjects were actively drinking, they were all breathalyzed on arrival and were negative for alcohol, so this appears to be a carryover effect of recent alcohol consumption. Another key difference between the present study and previous data on melatonin and alcohol was we used plasma melatonin and not salivary melatonin, since levels of melatonin are 10-fold higher in the plasma compared with saliva (14).…”

Arginine metabolism: nitric oxide and beyond

“…Rat aortic endothelial cells and murine macrophages express both type I and type II arginases [200][201][202], and it is likely that other cell types also express both isoenzymes. The different subcellular localization of the arginase isoenzymes may provide a mechanism for regulating the metabolic fate of arginine, as postulated for enterocytes [203]. For example, differential expression of the arginase isoenzymes could provide a means to preferentially direct ornithine either to proline or glutamate synthesis via OAT or to polyamine synthesis via ODC (Figure 2).…”

Development of hamster circadian rhythms: Role of the maternal suprachiasmatic nucleus

“…Although there is little reason to expect that the normal development of circadian rhythms requires exposure to a rhythmic environment during development (Davis and Menaker 1981), being born to and raised by an SCN-lesioned mother in dim constant light represents the most constant Table 1. Midnight is indicated by O at the top of each circle and the times of day when pups were weaned are indicated by W. If the mother's rhythm was not disrupted by the lesion, her phase at weaning is indicated by M environment yet produced for the development of mammalian circadian rhythms.…”